Testing device



March 13, 1951 JACKSON 2,544,685

TESTING DEVICE Filed Feb. 20, ,1946 2 Sheets-Sheet 1 D/SGHARGE DEV/0E FRANK H. J21 6% am (7 I)? v". ID- V/ MA ATTORNEY March 13, 1951 Filed F'eb. 20, 1946 F. H. JACKSON TESTING DEVICE 2 Sheets-Sheet 2 INVENTOR ATTORNEY furnishes filament current for tube 35 and a secondary winding 3! furnishes filament current for Thyratron 23a. The high-potential supply line is connected to a center tap on secondary 36. The filtering arrangement comprises series chokes 38, 39 and shunt condensers 40, 41! and 42. Unit [8' also includes a voltage-regulating output circuit comprising a conventional voltage regulating tube 44 in series with a resistor 45 and a variable series resistor 46. Since it is desired to apply a known potential across terminals l4, for charging the R-C circuit, terminal 14 is coupled to the anode of voltage regulating tube 44 though a first blade and set of contacts of switch 29 and terminal I5 is grounded by conductor 41.

Since it is necessary to employ the potential between terminals l5 and It to break down discharge device 26 and to trip relay 26a, 23b, terminal i6 is connected to the cathode of tube 26' to hold the cathode more positive than the starting anode. The main anode is not used. During the resetting operation the junction of the connections from terminal l6 and the cathode of tube 26 is connected through a resistor 48 and a first set of contacts and blade of switch 3! to ground, so that condenser ll discharges. During the measuring operation the potential between terminals l5 and It appears across resistor 48 and the high impedance of the cathodestarting anode circuit of tube 26', efiectively entirely across the latter by virtue of its high resistance.

Upon breakdown of tube 26' substantially all of the last-mentioned potential appears across a resistor 49, connected between the starting anode of tube 26 and ground, since the tube impedance decreases and the potential drop between the cathode and starter anode is then negligible. The potential appearing across resistor 49 is utilized to render a control electrode of tube 23a more positive. This electrode is normally biased negatively by unit I8 through a circuit, comprising a series arrangement of resistor 5| and variable resistor 52, between the high voltage terminal of unit l8 and ground. To this end, the cathode of tube 23a. is connected to a desired point on resistor 52. The tap on resistor 52 and therefore the cathode of tube 28a are biased to be more positive than that terminal of resistor 49 remote from ground and therefore more positive than the control electrode of tube 23a.

Upon breakdown of tube 26', the potential across resistor 49 overcomes this bias, since the junction of resistor 49 and th starter electrode of tube 26 is connected to the controlelectrode of the Thyratron tube. Tube 23a is according- 1y triggered and it becomes conductive. Tube 23a also includes a shielding electrode connected to its cathode.

The plate current flowing in tube 23a causes this sequence of events: (1) the winding of relay 23b is excited and contact 25 is separated from contact 24 and attracted to the magnetic core disposed within the relay winding; (2) the circuit between the 110 volt source and the magnetic clutch, is broken; (3) the magnetic clutch is deenergized; and (4) clock 20 stops. -In order to accomplish these objectives, the anode of tube 23a is connected, through a second set of contacts and blade of switch 3|, the winding of relay 23b and a dropping resistor 54,'to the high-potential side of power supply I8. The tube discharge path is completed by connecting the cathode of tube 23a to ground. through a portion of resistor 52, and thus to the ground side of unit I8.

After a measurement has been taken it is desired to set up the device for another operation. This requires the discharge of condenser II and the stopping of anode current in tube 230.. Accordingly, there is provided a resistor 48 in a series circuit comprising terminal 5, the firstmentioned blade and set of contacts of switch 3! and ground. During the measurement operation this circuit is open and the second set of switch 3! contacts (in series with relay 23b) is initially closed. However, when the resetting operation is performed, the latter set of contacts is opened and the first set of contacts (in series with resistor 48) is closed. Since terminals l5 and iii are then effectively short-circuited by resistor 48, condenser H discharges. Moreover, the plate circuit of tube 23a is then open and anodecurrent flow ceases.

While it is not proposed that the invention be limited to any specific circuit dimensions, the following component characteristics have been found practicable in one successful embodiment of the type illustrated in Fig. 2.

Component Characteristic Input voltage to unit l8 volts, alternating current, 60

cycles per second. Tube 35 5W4. Ghokes 38 and 39 15 henries. Condensers 40, 41 and 42 8 microfarads. Tube 26 Type OA4-G. Tube 23" Type 2051. Resistor 54 25,000 ohms. Resistor 48 2,000 ohms. Resistor 49-. 20,000 ohms. Resistor 52 5,000 ohms. Resistor 51 200,000 ohms. Resistor 46 10,000 ohms. Resistor 45 10,000 ohms. Supply voltage to clock 110 volts alternating current 60 cycles per second. Switch 19 Two-gang. Switch 31 0. Tube 44 Type 874 or Type VRQO.

Referring now to the operation of the device illustrated in Fig. 2, it will be assumed that contacts 24 and 25 are in circuit, that relay 23b is deenergized, that switch l9 is open, that switch 3! is in the measuring position, that resistor 48 is out of circuit, that the testing device is suitably connected to the sample [0 to be tested, and that tube 23a is biased to a nonconductive state by the flow of current from unit It through resistor 52. Since switch i9 is open magnetic clutch 21 is not excited and clock 20 is stopped.

Upon the closing of switch l9 an electromotive force is applied between terminals 94 and I5 and condenser l l begins to charge. Simultaneously the .magnetic clutch is energized and clock 20 begins to run. Upon the attainment of the predetermined magnitude of potential across condenser H, the voltage between terminals l5 and i6 is sufiicient to break down tube 26 and substantially the whole of that voltage appears across resistor 49, rendering the control electrode of tube 23a more positive. The later tube is accordingly tripped and anode current flows therein, energizing the winding of relay 23b and breaking the circuit between contacts 24 and 25.

Accordingly, the magnetic clutch winding is opencircuited and clock 20 stops. This occurs at the same instant as the attainment of the aforementioned predetermined potential across condenser ll. Therefore, clock 20 effectively measures the time of charge of condenser ll.

While there have been shown and described what are at present considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various modifications and changes may be made therein without departing from the true spirit of the invention. For example a neon lamp with the startin resistor removed may be substituted for the cold-cathode tube 26'. It is accordingly intended in the appended claims to cover all such changes and modifications as fall within the true scope of the invention and without the prior art.

I claim:

1. A testing device for measuring the time of charging of a capacitor through a resistance to a predetermined potential comprising a timer having an electrically operated control element adapted to start the timer when energized and V to stop the timer when de-energized, means for simultaneously applying electric potentials to the control element to start the timer and to the capacitor under test through the resistor under test to begin charging said capacitor, and means to de-energize said control element to disable said timer including a gas-filled electron tube coupled to the capacitor under test and adapted to break down when said capacitor is charged to said predetermined potential, and also including means responsive to the breakdown to open the circuit to said control element, whereby said timer measures the time for charging said capacitor through said resistance to said predetermined potential.

2. A testing device in accordance with claim 1 in which the timer includes a drive mechanism and an indicating mechanism, and the electrically operated clutch element consists of a magnetic clutch for connecting said mechanisms.

3. A testing device in accordance with claim 1 and in which the means to open the circuit to said control element includes a relay.

4. A testing device in accordance with claim 1 and in which the means to open the circuit to said control element comprises a relay and a second gas-filled tube for actuating the relay.

5. A testing device for measuring the time of charging of a capacitor through a resistance to a predetermined potential, comprising a timer having an electrically operated control element adapted to start the timer when energized and to stop the timer when de-energized, means for simultaneously applying electric potentials to the control element to start the timer and to the capacitor under test through the resistor under test to begin charging said capacitor, an impedance coupled to said capacitor and including the interelectrode breakdown path through a glow discharge tube in which the impedance of said breakdown path decreases abruptly when the voltage across said capacitor reaches said predetermined potential, and means triggered by said decrease in impedance to open the circuit to said control element, whereby said timer measures the time for charging said capacitor through said resistance to said predetermined potential.

6. A testing device for measuring the time of charging of a capacitor through a resistance to a predetermined potential, comprising a timer havin an electrically operated control element adaptedto start the timer when energized and to stop the timer when de-energized, means for simultaneously applying electric potentials to the control element to start the timer and to the capacitor under test through the resistor under test to begin charging said capacitor, an impedance coupled to said capacitor and including the cathode-starter electrode breakdown a path of a cold-cathode electron tube which will break down when the voltage across said capacitor reaches said predetermined potential, a gasfilled, grid-controlled electron tube coupled to a portion of said impedance and adapted to be triggered by the potential appearing in said portion upon breakdown of said path, and a relay coupled to said grid-controlled tube and responsive to the discharge current thereof to open the circuit to said control element, whereby said timer measures the time for charging said capacitor through said resistance to said predetermined potential.

FRANK H. JACKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,332,844 Kasson Mar. 2, 1920 2,010,968 Smith Aug. 12, 1935 2,044,424 Edwards et al June 16, 1936 ,212,981 Dorsett et a1. Aug. 27, 1940 2,408,727 Blitz Oct. 8, 1946 2,504,848 Kunz Apr. 18, 1950 FOREIGN PATENTS Number Country Date 551,910 Great Britain Mar. 15, 1943 

